Fossil Friday: More Evidence That “Feathered Dinosaurs” Were Secondarily Flightless Birds
in one of my recent Fossil Friday articles (Bechly 2024) I elaborated on the neoflightless hypothesis by paleo-ornithologist Alan Feduccia, who convincingly argues that all those feathered bipedal “dinosaurs” are in fact not related to theropod dinosaurs at all but rather represent secondarily flightless birds. I also discussed new evidence that strongly supports this view. Indeed, Agnolin et al. (2019) already commented in their study on the dinosaur-bird transition:
In a ground-breaking proposal, Xu et al. (2011) hypothesized that Archaeopteryx was more nearly related to deinonychosaurians than to birds and that deinonychosaurs become secondarily flightless, a hypothesis previously envisaged by Paul (2002). This hypothesis was supported by a variety of more recent analyses (Godefroit et al., 2013a; Xu et al., 2015; Hu et al., 2018).
Yet Another Discovery
After my article was published (Bechly 2024), I stumbled upon yet another discovery that may lend additional support to Feduccia’s hypothesis:
Just about a decade ago, Godefroit et al. (2013b) described a new supposed theropod dinosaur from the Middle-Late Jurassic Tiaojishan Formation of Liaoning in China. With an estimated age of 160 million years it is 10 million years older than the famous Archaeopteryx. They named the new species Eosinopteryx brevipenna, because of its reduced plumage. The single known specimen (an artist’s depiction of the living animal is above, or see here for the fossil) represents a very well-preserved fossil and almost complete skeleton, which allowed scientists to identify the new taxon as a close relative of the feathered dinosaur Anchiornis.
But this generated a problem: the new dinosaur appeared to be nested deeply in the tree of feathered dinosaurs, so that its reduced plumage cannot be a primitive state but has to be a secondary reduction from a more complete set of feathers. Furthermore, the bone structures of the shoulder articulation showed that the animal was not capable of flapping its arms or wings. This is even more perplexing, as this case of reduced flight adaptations predates the famous missing link Archaeopteryx. Consequently, the press release to the new study (University of Southampton 2013) announced that this fossil “challenges bird evolution theory” and suggested “that the origin of flight was much more complex than previously thought.” The lead author, Dr. Gareth Dyke from the University of Southampton, is quoted with this remarkable admission: “This discovery sheds further doubt on the theory that the famous fossil Archaeopteryx — or “first bird” as it is sometimes referred to — was pivotal in the evolution of modern birds.”
Challenged by Other Evolutionists
Don’t hold your breath, though, waiting for textbooks to be updated accordingly, because this confounding result was quickly challenged by other evolutionist scientists. They claimed that the distinct features of Eosinopteryx could rather be based on variability of the plumage and incomplete preservation of the tail, so that it could even represent the very same species as Anchiornis huxleyi (Pei et al. 2017, Hu et al. 2018, Agnolin et al. 2019). But these studies partly disagreed on certain crucial issues, such as the question of whether the shorter tail in Eosinopteryx is complete and diagnostic (Pei et al. 2017) or not (Hu et al. 2018, Agnolin et al. 2019). Moreover, other experts had recorded further diagnostic differences between the skeletons of two taxa, such as anteriorly convex pubic shafts that are present in Anchiornis but absent in Eosinopteryx (Foth & Rauhut 2017), or the length and shape of the prefrontal and maxillary processes (Guo et al. 2018). Also the cladistic studies by Lefèvre et al. (2014), Guo et al. (2018), Hu et al. (2018), and Pei et al. (2020) did not recover Eosinopteryx as closest relative of Anchiornis, or even rejected the monophyly of Anchiornithidae. One could almost get the impression that the desire to explain away inconvenient results may have guided the interpretations of those scientists, who denied the distinctness of Eosinopteryx.
There are clearly open questions and it definitely looks like the common dino-to-bird narrative has been massively oversold to the public and represents a theory with numerous holes and problems.
References
Agnolin FL, Motta MJ, Brissón Egli F, Lo Coco G & Novas FE 2019. Paravian Phylogeny and the Dinosaur-Bird Transition: An Overview. Frontiers in Earth Science 6: 252, 1–28. DOI: https://doi.org/10.3389/feart.2018.00252
Bechly G 2024. Fossil Friday: New Study Confirms “Feathered Dinosaurs” Were Secondarily Flightless Birds. Evolution News April 5, 2024. https://evolutionnews.org/2024/04/fossil-friday-new-study-confirms-feathered-dinosaurs-were-secondarily-flightless-birds/
Foth C & Rauhut OWM 2017. Re-evaluation of the Haarlem Archaeopteryx and the radiation of maniraptoran theropod dinosaurs. BMC Evolutionary Biology 17: 236, 1–16. DOI: https://doi.org/10.1186/s12862-017-1076-y
Godefroit P, Cau A, Dong-Yu H, Escuillié F, Wenhao W & Dyke G 2013a. A Jurassic avialan dinosaur from China resolves the early phylogenetic history of birds. Nature 498(7454), 359–362. DOI: https://doi.org/10.1038/nature12168
Godefroit P, Demuynck H, Dyke G, Hu D, Escuillié F & Claeys P 2013b. Reduced plumage and flight ability of a new Jurassic paravian theropod from China. Nature Communications 4(1): 1394, 1–5. DOI: https://doi.org/10.1038/ncomms2389
Guo X, Xu L & Jia S 2018. Morphological and Phylogenetic Study Based on New Materials of Anchiornis huxleyi (Dinosauria, Theropoda) from Jianchang, Western Liaoning, China. Acta Geologica Sinica – English Edition 92(1), 1–15. DOI: https://doi.org/10.1111/1755-6724.13491
Hu D, Clarke JA, Eliason CM, Qiu R, Li Q, Shawkey MD, Zhao C, D’Alba L, Jiang J & Xu X 2018. A bony-crested Jurassic dinosaur with evidence of iridescent plumage highlights complexity in early paravian evolution. Nature Communications 9(1): 217, 1–12. DOI: https://doi.org/10.1038/s41467-017-02515-y
Lefèvre U, Hu D, Escuillié FO, Dyke G & Godefroit P 2014. A new long-tailed basal bird from the Lower Cretaceous of north-eastern China. Biological Journal of the Linnean Society 113(3), 790–804. DOI: https://doi.org/10.1111/bij.12343
Paul GS 2002. Dinosaurs of the Air: The Evolution and Loss of Flight in Dinosaurs and Birds. The John Hopkins University Press, Baltimore (MD), 472 pp.
Pei R, Li Q, Meng Q, Norell MA & Gao K-Q 2017. New Specimens of Anchiornis huxleyi (Theropoda: Paraves) from the Late Jurassic of Northeastern China. Bulletin of the American Museum of Natural History 411, 1–67. DOI: https://doi.org/10.1206/0003-0090-411.1.1
Pei R, Pittman M, Goloboff PA, Dececchi TA, Habib MB, Kaye TG, Larsson HCE, Norell MA, Brusatte SL & Xu X 2020. Potential for Powered Flight Neared by Most Close Avialan Relatives, but Few Crossed Its Thresholds. Current Biology 30(20), 4033–4046.e8. DOI: https://doi.org/10.1016/j.cub.2020.06.105
University of Southampton 2013. Discovery of ‘Bird-Dinosaur’ Eosinopteryx Challenges Bird Evolution Theory. SciTechDaily January 24, 2013. https://scitechdaily.com/discovery-of-bird-dinosaur-eosinopteryx-challenges-bird-evolution-theory/
Xu X, You H, Du K & Han F 2011. An Archaeopteryx-like theropod from China and the origin of Avialae. Nature 475(7357), 465–470. DOI: https://doi.org/10.1038/nature10288
Xu X, Zheng X, Sullivan C, Wang X, Xing L, Wang Y, Zhang X, O’Connor JK, Zhang F & Pan Y 2015. A bizarre Jurassic maniraptoran theropod with preserved evidence of membranous wings. Nature 521(7550), 70–73. DOI: https://doi.org/10.1038/nature14423
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